1. Field of the Invention
The invention relates to battery connecting tabs and in particular to battery connecting tabs made of two different materials.
2. Description of Prior Art
Batteries are commonly used in portable devices. It is necessary to connect a plurality of batteries in series or parallel, forming a high current charging and discharging battery module, for supplying a required power of large electronic equipment, such as electric cars. Generally, one of the methods for connecting batteries in series or parallel is to use connecting tabs connecting across the electrodes of adjacent two batteries, and form a current loop by welding the connecting tabs to batteries.
Please refer to FIG. 8. FIG. 8 shows schematically a perspective view of the battery connecting tabs connecting with the batteries of prior art. A battery 200 case (including electrodes) is generally made of pure nickel, iron plated by nickel or aluminum for preventing the active materials contained in the battery 200 to contact directly to the external materials. It has an advantage of easily welding electrodes 210 and battery connecting tabs 100 when the connecting tabs 100 uses the same material with the case of the battery 200. However, the conductivity of pure nickel, iron plated by nickel or aluminum is poor, they are not suitable to use in the high current charging and discharging battery module.
Battery connecting tabs 100 made of copper are usually used in the high current charging and discharging battery module due to their excellent conductivity. Because of the need of supplying battery module high current at the time of charging and discharging, it is required to increase the thickness of battery connecting tabs made of copper for upgrading the conductivity. However, it may cause the welding difficulty of the battery 200 and the battery connecting tabs 100 as the thickness of the battery connecting tabs increases. The main reason is that the thickness of the battery connecting tabs 100 is increased, the higher welding current is required, and the greater stress is also needed, and thus it is difficult to control process parameters. Also, the thermal energy provided by a specific welding temperature is not easy to concentrate because of the large heat dissipation area, which causes that the welding quality is difficult to control.
Moreover, copper may soon dissipate the heat on its surface when welding due to its good thermal conductivity. Therefore, it causes a problem that the heat can not be concentrated on a specific area of the surface of copper when welding, and it is difficult to weld by copper.
Thus, it would be highly desirable to have battery connecting tabs 100 which have excellent electrical conductivity and thermal conductivity, and are easy to connect with batteries 200 which are used in a high current charging and discharging battery module.